软沉积物变形构造研究进展

RESEARCH PROGRESS OF SOFT-SEDIMENT DEFORMATION STRUCTURES

本文对软沉积物变形构造的相关研究进展进行简要综述。软沉积物变形构造广泛发育于沉积地层中,对其形成过程的正确解释在理解沉积盆地的充填机制和性质、油气储层勘探,以及与其相关的沉积岩相和地层序列的解释等方面具有一定的指导意义。由此,对软沉积物变形构造的研究也成为近20年来沉积学的热点之一。软沉积物变形构造主要由液化或流化、反密度梯度、重力滑塌及剪切力等作用形成。碳酸盐沉积物在成岩过程早期由于较易于受到海水方解石的胶结作用而常呈固结或半固结状态,在外力触发下,会出现破裂、移位而形成竹叶状灰岩或碳酸盐岩块体;颗粒质碳酸盐沉积物由于不均匀胶结作用,也会出现差异液化现象,形成砾屑灰岩。地震是较为普遍的触发机制,但一些研究发现很多潮坪沉积、风暴沉积中的软沉积物变形构造可能是由潮汐涌潮和风暴作用触发而成,因此在解释软沉积物变形机制时要在对沉积过程、沉积环境和构造背景等做系统研究的基础上进行综合分析论证。

Soft-sediment deformation structures(SSDS) often occur in sedimentary successions. Proper interpretation of their formative processes may provide important implications for basin-filling mechanisms, exploration of petroleum reservoirs, and understanding of depositional processes. Therefore, studies on SSDS have become popular in the field of sedimentology and stratigraphy. SSDS form mainly by liquefaction and fluidization, reverse density gradient, gravitational slumping, and shear. Carbonate sediments, in contrast to siliciclastics, are more susceptible to early marine calcite cementation, and become(semi) consolidated soon after deposition. These(semi) consolidated carbonate sediments may be fragmented and further mobilized under external forces, forming carbonate breccias and blocks. Grainy carbonate sediments may be heterogeneously cemented and thus be differentially liquefied, forming carbonate breccias of well cemented, unliquefied sediment, with liquefied portion being the matrix. Earthquake is a common trigger for SSDS, but quite a few studies show that SSDS in sediment on tidal settings and tempestites, for example, may be triggered by tidal bore and storm-wave loading, respectively, rather than earthquakes. Interpreting formative mechanisms and triggers of SSDS requires integrative studies on sedimentary processes, depositional environments, and tectonic settings.